ITMI941838A1 - HIGH MECHANICAL RESISTANCE PAPER AND CARDBOARD PRODUCTION PROCESS - Google Patents

Description

The present invention refers to a process for the production of paper and cardboard with high mechanical resistance.

It is known that, during the production of paper and cardboard, the addition of starches to the cellulose mixture improves the mechanical properties of the finished product (in particular the resistance to dryness and bursting). The addition of starches is therefore particularly advantageous when partially degraded cellulose is used as raw material, such as that deriving from recycled paper products. As is known, natural starch per se has little affinity for cellulose fibers and for the fillers contained in the mixtures. The result is a bad retention and therefore an enrichment of starch in the machine circuits, as well as a certain deterioration in the drainage, a bad functioning of the recovery devices and an increase in the Chemical Oxygen Demand (COD) and the Biological Oxygen Demand (BOD) of the effluents after prolonged use.

For these reasons, paper manufacturers have turned to the use of modified starch, in particular cationic starch. This is prepared by reacting natural starch in a basic environment with a suitable cationized agent, for example amines or ammonium salts, such as (diethyl-2-chloroethyl) ammonium chloride or (epoxypropyltrimethyl) ammonium chloride. The use of cationic starch generally leads to good results, but involves a considerable increase in production costs.

In US patent 4,818,341, a process for the manufacture of paper and cardboard is described, in which a mixture consisting of natural potato starch and a particular cationic polymer comprising units of (a) diallyldimethylammonium chloride is used as a reinforcer and binder. ; (b) N-vinylamine; or (c) an N-vinylimidazoline. Also in this case, the use of particular cationic polymers makes the process economically disadvantageous, especially for large-scale production and / or starting from poor quality cellulosic raw materials (for example recycled paper).

The Applicant has now surprisingly found that the retention of natural starch on the cellulose fibers can be considerably increased, up to levels comparable to those obtainable with a cationic starch, if an iron and / or iron salt is added to the cellulose mixture. aluminum. It has also been found that retention is considerably higher if the natural starch is previously mixed with the aluminum and / or iron salt, and the resulting mixture is then added to the cellulose slurry.

Therefore, the subject of the present invention is a process for the production of paper and cardboard, which comprises adding to the cellulose mixture a natural starch and an aluminum and / or iron salt. The cellulose mixture thus obtained is then subjected to drainage and subsequent calendering according to conventional techniques.

Natural starch means starch directly obtained from a natural source, such as wheat, corn, rice, potato, and the like. In a preferred embodiment, the natural starch is previously subjected to a pregelatinization treatment, i.e. cooking of an aqueous suspension of starch at a temperature higher than the gelatinization temperature of the starch itself, so as to make the latter water-soluble. (with formation of the so-called starch weld). By gelatinization temperature is meant the temperature at which the disappearance of the birefringence effect of the starch grains is observed (see the aforementioned patent US-4,818,341). It varies according to the type of starch considered and is generally between 70 ° and 110 ° C.

The aluminum and / or iron salts can in particular be chosen from:

(i) aluminum polychloride, having formula

or formula where the molar ratio 0H / 3A1 is generally comprised between 0.2 and 0.8, preferably between 0.35 and 0.6;

(ii) aluminum sulphate A12 (S04) 3;

(iii) FeC13 ferric chloride;

(iv) FeC1S04 ferric chlorosulfate.

Particularly preferred is the aluminum polychloride. As already mentioned above, in a preferred embodiment the natural starch and the aluminum and / or iron salt are used in a mixture, for example according to the following procedure:

(a) preparing an aqueous solution of natural starch by heat, according to known techniques, thus obtaining the so-called starch weld (pre-gelatinization process, see above);

(b) dissolve the aluminum and / or iron salt in the starch solution,

(c) feeding the mixture thus obtained into the pulp pulp used for the production of the paper.

The concentration of the starch weld prepared in step (a) is generally comprised between 0.5 and 10% by weight, preferably between 1 and 5% by weight. Step (b) of dissolving the salt in the starch weld is generally carried out at a temperature between 15 ° and 160 ° C, preferably between 30 ° and 80 ° C, for times usually between 0.1 and 60 min, preferably between 1 and 20 min.

The aluminum and / or iron salt, expressed as Me203 oxide (Me = Al, Fe), is added to the starch in quantities generally comprised between 5 and 90, preferably between 10 and 60, parts by weight per 100 parts of starch. For aluminum polychlorides, the amount is preferably comprised between 10 and 30 parts by weight.

The natural starch is added to the cellulose slurry in quantities generally comprised between 0.1 and 10% by weight, preferably between 0.3 and 6% by weight, more preferably between 0.5 and 3% by weight, with respect to dry cellulose.

The process object of the present can be used for the production of any type of paper or cardboard, starting from a wide variety of cellulosic fibers, for example from sulphite or sulphate pulp, subjected to a bleaching process or as such, from thermo-mechanical (TMP) or chemothermomechanical (CTMP) pulps, or even from recycled cellulosic fibers, possibly subjected to de-inking processes, or from blends of virgin and recycled fibers, etc.

Some examples of embodiment of the present invention are reported below, the purpose of which is purely illustrative but not limitative of the scope of the invention itself.

EXAMPLE 1

Preparation of the cellulose fiber mixture.

320.5 g of bleached softwood sulfite cellulose and 320.5 g of bleached broadleaf sulfate cellulose were pulped in a laboratory pulper in 121 of water for 30 minutes, obtaining a 5% dry weight slurry. 131 of water was added to this mixture, so as to obtain a mixture with 2.5% by weight of dry matter. This mixture was then refined in a Dutch Valley laboratory refiner, until a degree of refinement of 30 ° SR was obtained, measured by a Riegler Shopper device. After refining, 4 kg of mixture were added, under stirring, to 161 of water, so as to obtain a mixture with 0.5% by weight of dry product, to be used in subsequent processing.

Preparation of starch.

47.5 g of natural corn starch was added, at room temperature and under stirring, to 952.5 g of water. Still under stirring, the starch suspension was gradually brought to a temperature of 92 ° -96 ° C and kept at this temperature for 20-30 minutes, until the starch was cooked. The weight was then brought back to 1000 g by adding more water. The starch weld thus obtained had a concentration equal to 4.75% by weight.

Preparation of the starch / PAC mixture.

84.0 g of the starch solution prepared as above, kept at 70 ° C, was added with 2.47 g of type B polychloride aluminum (PAC) (PAC-B, see Table 2). Water was then added until a total weight of 100 g was obtained. After stirring for 1 min, a mixture was obtained containing 2.47% by weight of PAC-B and 4.0% by weight of starch, calculated on a dry basis.

Addition of the starch / PAC mixture to the cellulose slurry.

7.5 g of the starch / PAC mixture prepared as above was added to 1 kg of 0.5% cellulosic mixture prepared as described above, placed under stirring by means of a Jar Test apparatus operating at 200 rpm, in order to have a quantity of starch, calculated on the dry basis, equal to 6.0% by weight, and a quantity of PAC-B equal to 3.7% by weight, the percentages being calculated with respect to the quantity of dry cellulose present in the mixture. After 3 minutes of stirring, the degree of starch retention by the cellulosic fibers was evaluated by means of COD measurements according to the following method.

400 g of the dough was taken and placed in a Riegler Shopper machine. After 5 seconds, the inverted cone cap was lifted and the waste water was collected through the non-calibrated side hole, after having previously closed the calibrated central hole and filled with water. On 25 ml of this waste water the COD was determined by oxidation with potassium dichromate in an acid medium and titration with ferrous sulphate, according to the method described by N.W. Hanson in "Officiai, Standardized and Recommended Methods of Analysis" (page 383, The Society for Analytical Chemistry, 1973). Obviously, the lower the measured COD value, the greater the retention of the anudo by the cellulose fibers. The results are reported in Table 1, where the value of ΔCOD% is also indicated, i.e. the percentage difference in the COD of the waste water compared to the test in which natural starch without PAC was used (Example 5) . The COD value of the starch weld at the concentration of use (300 ppm) was 304 mg / 1, while the COD of the starting cellulosic mixture was 74 mg / 1.

EXAMPLE 2

Example 1 was repeated under the same conditions, except that the two separate components were added to the cellulosic mixture, instead of adding the previously prepared starch / PAC mixture, in such quantities as to obtain the same% by weight with respect to to the dry cellulose: 6.3 g of the starch compound at 4.75% by weight were first added to 995.6 g of mixture, after 3 min of stirring 0.185 g of PAC-B; finally the mixture, consisting of water, cellulose, starch and PAC-B, was stirred for a further 3 min in the Jar Test apparatus. The measured COD values are shown in Table 1.

EXAMPLES 3-4

Examples 1 and 2 were repeated under the same conditions, but using a double quantity of PAC-B (7.4% by weight on the dry cellulose). The results are reported in Table 1.

EXAMPLE 5 (comparative)

Example 1 was repeated under the same conditions, but using only starch without adding PAC. The results are reported in Table 1.

EXAMPLES 6-15

Examples 3 and 4 were repeated under the same conditions using the different salts reported in Table 2: PAC-A (Ex. 6-7), PAC-C (Ex. 8-9), aluminum sulphate (AS) (Ex.

10-11), ferric chloride (CF) (Ex. 12-13), and ferric chlorosulfate (CSF) (Ex. 14-15). The amount of added salt, expressed as% by weight of Me203 oxide (Me = Al, Fe) with respect to the weight of the dry cellulose, is in all examples equal to 1.33%, equal to that of Examples 3-4. The quantities used and the COD values measured on the waste water are shown in Table 3.

EXAMPLES 16-18

Example 3 was repeated by varying the amount of starch present in the starch / PAC-B mixture (4.0% by weight in Example 3). The results are reported in Table 4.

EXAMPLES 19-22

Example 18 was repeated by varying the temperature at which the preparation of the starch / PAC-B mixture was carried out (70 ° C in Example 18). The results are reported in Table 4.

EXAMPLES 23-27

Example 18 was repeated by varying the stirring time for the preparation of the starch / PAC-B mixture (1 min in Example 18). The results are reported in Table 4.

subsequently diluted with water to obtain a concentration of 0.5% by weight on the dry basis. The results are reported in Table 6.

EXAMPLES 49-51

Examples 3-5 were repeated using natural potato starch instead of natural corn starch. The results are reported in Table 7.

Claims (15)

CLAIMS Process for the production of paper and cardboard starting from a pulp of cellulose, which comprises adding to said mixture a natural starch and an aluminum and / or iron salt. Process according to claim 1, wherein natural starch is a starch directly obtained from wheat, corn, rice, potato, and the like. Process according to any one of the preceding claims, in which the natural starch is previously subjected to a pre-gelatinization treatment. Process according to any one of the preceding claims, in which the aluminum and / or iron salts are selected from: (i) aluminum polychloride, having formula or formula where the OH / 3A1 molar ratio is between 0.2 and 0.8; (ii) aluminum sulfate (iii) ferric chloride (iv) ferric chlorosulfate. Process according to claim 4, wherein the aluminum and / or iron salt is aluminum polychloride (I). Process according to any one of the preceding claims, in which the natural starch and the aluminum and / or iron salt are added to the cellulose slurry in mixture. 7. Process according to claim 6, wherein the natural starch and the aluminum and / or iron salt are added to the cellulose slurry according to the following procedure: (a) hot preparing an aqueous solution of natural starch, obtaining a starch weld; (b) dissolve the aluminum and / or iron salt in the starch solution; (c) feeding the mixture thus obtained into the pulp pulp used for the production of the paper. 8. Process according to claim 7, wherein the concentration of the starch weld prepared in step (a) is comprised between 0.5 and 10% by weight. 9. Process according to claim 7, wherein the step (b) of dissolving the salt in the starch weld is carried out at a temperature comprised between 15 ° and 160 ° C, for times comprised between 0.1 and 60 min. 10. Process according to claim 7, in which the aluminum and / or iron salt, expressed as Me203 oxide (Me = Al, Fe), is added to the starch in quantities ranging from 5 to 90 parts by weight per 100 parts of starch. 11. Process according to claim 7, wherein in step (b) as the aluminum salt polychloride of aluminum (i) is used in quantities, expressed as oxide Al203, comprised between 10 and 30 parts by weight per 100 parts by weight of starch . Process according to any one of the preceding claims, in which natural starch is added to the cellulose mixture in quantities ranging from 0.1 to 10% by weight, with respect to the dry cellulose. 13. Process according to claim 12, in which natural starch is added to the cellulose slurry in quantities ranging from 0.3 to 6% by weight, with respect to the dry cellulose. 14. Process according to claim 13, in which natural starch is added to the cellulose slurry in quantities ranging from 0.5 to 3% by weight, with respect to the dry cellulose. 15. Process according to any one of the preceding claims, in which the cellulosic mixture is constituted by cellulose pulp with sulphite or sulphate, by thermomechanical (TMP) or chemothermomechanical (CTMP) cellulose pulps, by recycled cellulosic fibers, possibly subjected to de-inking processes, or from blends of virgin and recycled fibers.